It has been known to use for steering streetcars a rail system wherein, parallel to each rail on which the wheels are rolling, a guide rail is arranged in which guide rollers are running which are mounted at the car body (DE-A-473 106). The inside of the bogie wheel is provided with a flange, while no flange is provided at its outside. The guide rollers may be lifted individually from the appertaining guide rail by control through magnetic coils. At the junctions or switch-points of the rail system, the guide rollers which are engaging a guide rail cause the steering of the associated bogie so that the streetcar is following the corresponding rail track which is predetermined by the active guide rollers. By this means, ground switchpoints with adjustable tongues are unnecessary. However, when a rail track is used that branches off a straightly extending continuous track, the treads of the outer wheels do not rest any longer on the rail for a longer distance of the path. In addition, said system cannot be used for vehicles running on one sole rail only because no lateral guidance is ensured with wheels having only one sole flange.
There has been also known a rail-guided servicing system (DE-C-21 00 854) wherein the vehicles extend between the ground rail and an upper rail. The bogie wheel or bogie wheels of a vehicle are guided in the U-shaped ground rail. In the direction of travel in advance of the bogie wheels, lateral guide rollers are mounted which, at junctions or branchings of the rail system, can be lowered individually in respective guide rails which extend laterally along the main rails. Similar guide rollers are provided at the upper rail system. The guide rollers at the ground rail system and at the upper rail system are controlled synchroneously thus avoiding a divergence between the upper and lower guide paths of the vehicle. The single rail conveying system (i.e. including one sole ground rail) is used as a transportation means for storage racks. The vehicles may travel on floors between racks in a storehouse. They are provided with a lifting structure at which a platform movable vertically is guided to lift loads to the height of the required rack shelves. It is again disadvantageous in this known system that the bogie wheels are not guided laterally with a sufficient accuracy over a considerable distance in case of junctions or switchpoints because the flanges of the U-shaped ground rail are divergent in said area.
It is the object of the invention to provide a rail-guided transportation system of the above mentioned type wherein the exact guiding of the bogie wheels is possible in case of junctions or branchings the interruption of the rail profile being reduced to a minimum.